The invention relates to a continuously operated gas analyser comprising:
a) a detector which is dependent upon the mass flow of the gas to be analyzed,
b) a suction device at the detector output,
c) a vacuum regulating circuit which is connected to the detector output and which maintains constant the vacuum p.sub.3, generated by the suction device, at the detector output in relation to the atmospheric pressure p.sub.o,
d) a first choke which is connected in advance of the detector in the pipe-line for the gas to be measured,
e) a second choke which is connected in parallel to the series arrangement of the first choke and the detector as a by-pass,
f) a third choke which is connected in advance of the common gas inlet and
g) a further vacuum regulating circuit which is connected to the common connection point of the three chokes and which maintains constant the pressure p.sub.2 prevailing at said connection point in relation to the atmospheric pressure p.sub.o.
A gas analyser of this type which is operated under vacuum and is equipped with regulating circuits is described in U.S. Pat. No. 4,341,108. However, it has been established that the vacuum regulation requires improvement if more stringent demands are imposed on the measurement accuracy.